The application of heat to tissue, typically from a flame heated metal object, has been used for centuries to cauterize bleeding wounds. In cauterization, the essential mechanism behind tissue treatment involves raising the temperature of the bleeding tissue by conductive heat transfer from the heated metal object. In order to arrest bleeding from the tissue's severed blood vessels, the tissue is heated adequately to shrink certain tissue proteins, such as collagen, thus closing the blood vessels and ultimately leading to blood vessel thrombosis.
Apart from shrinkage, the application of compressive force from a heated metal object to a blood vessel may also result in collagen welding, such as for the permanent joining together of opposite walls of a blood vessel, thus providing another mechanism of hemostasis in addition to simple shrinkage of collagen.
With the aid of electricity, cauterization spurred the development of electrocautery devices to treat bleeding. While electrocautery devices still involve the use of a heated metal object, the electrocautery device is heated via electrical energy converted to heat in the metal object as opposed to heating the metal with a direct flame.
More recently, coagulation may be accomplished by radio frequency (“RF”) electrosurgical devices where electrical energy is converted to heat in the tissue rather than in the device. Heating of the tissue is often performed by means of resistance heating. In other words, increasing the temperature of the tissue as a result of electric current flow through the tissue which is resisted by the tissue. Electrical energy is converted into thermal energy (i.e. heat) via accelerated movement of ions as a function of the tissue's electrical resistance and current flow.
Hemostasis of the above sort is not without its drawbacks. Current dry tip RF electrosurgical devices can cause the temperature of tissue being treated to rise significantly higher than 100° C., thus exceeding the boiling temperature of inter-cellular water and resulting in tissue desiccation, tissue sticking to the electrodes, tissue perforation, char formation and smoke generation. Peak tissue temperatures at a targeted tissue treatment site can be as high as 320° C. as a result of RF treatment, and such high temperatures can be transmitted to adjacent untargeted tissue via conduction. Undesirable results of such transmission to untargeted adjacent tissue include unintended thermal damage to the untargeted tissue.
According to U.S. Pat. No. 6,086,586 to Hooven entitled “Bipolar Tissue Grasping Apparatus and Tissue Welding Method”, currently-available bipolar grasping instruments for electro-coagulation of tissue, or “tissue welding,” generally use only two electrodes of opposite polarity, one of which is located on each of the opposite jaws of the grasper. As illustrated in Hooven's FIG. 1, in use, tissue is held between a pair of grasper jaws (shown in cross-section) having first and second electrodes (Electrode 1 and Electrode 2) of opposite polarity. Bipolar current flows between the two electrodes along the illustrated current flow lines, with tissue coagulating first at the edges of the jaws. Then, as the tissue dries out and the impedance increases, the current flows through the moister tissue and the coagulation spreads both inward toward the center of the jaws and outward from the jaw edges.
The Hooven patent goes on to recite that “[t]hermal damage to adjacent structures can occur due to this spread of thermal energy outside the jaws of the instrument. Because of the spread of thermal energy outside the jaws of the instrument, it is difficult to coagulate long sections of tissue, such as bowel, lung, or larger blood vessels, without significant lateral thermal spread. Over-coagulation frequently occurs, resulting in tissue sticking to the jaws of the instrument. When the jaws of the instrument are opened, if the tissue sticking is severe, the tissue can be pulled apart, thus adversely affecting hemostasis.”
As part of the summary of the invention, the Hooven patent recites “a bipolar electrosurgical instrument having a pair of relatively moveable jaws, each of which includes a tissue contacting surface. The tissue contacting surfaces of the jaws are in face-to-face relation with one another, and adjacent each of the tissue contacting surfaces are first and second spaced-apart electrodes that are adapted for connection to the opposite terminals of a bipolar RF generator so as to generate a current flow therebetween.” Furthermore, the Hooven patent recites that, “[b]ecause each jaw is a bipolar electrode, multiple local current pathways, high current densities, and lower impediences are achieved. Indeed, the maximum current density is between the two insulated jaw surfaces, while a relatively lower current density exists at the electrode surfaces.”
However, the invention of the Hooven patent encounters certain difficulties. Due to tissue irregularities, the surface of the tissue to be treated may be uneven or undulated with peaks and valleys. Consequently, the area of electrical coupling of the tissue to the electrode surfaces can be limited to the isolated peaks in the tissue surface. In this situation, upon the application of RF power to tissue, the electrical coupling of only the tissue peaks to the electrode surfaces may result in corresponding increase in current density through the electrically coupled peaks which has the ability to desiccate and char the tissue at these isolated locations. Hooven does not address or provide for this situation.
Another difficulty encountered with the Hooven invention is that it does not address or provide for a decreasing electrical coupling between the tissue and electrode surfaces upon tissue shrinkage and/or desiccation during treatment. As tissue shrinks and/or desiccates during treatment, the tissue surfaces may loose contact with the electrode surfaces which, similar to above, decreases the area of electrical coupling therebetween and correspondingly increases the current density and associated heat at the locations which remain electrically coupled. This difficulty is further exacerbated if the tissue is undulated as described above.
Another difficulty encountered with the Hooven invention is that it does not address or provide for dissipating heat from the insulating members. Hooven does not address or provide how heat which may be conducted into the insulating members from the tissue between the two insulated surfaces is subsequently removed from the insulating members.
In light of the above, it is an object of the invention to provide devices, systems and methods which overcome the limitations of the art.